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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,297 records · Page 72
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NASA NTRS1985

The westward thermospheric jet-stream of the evening auroral oval

Ground-based and satellite measurements of the thermospheric wind in jet-streams during the evening auroral oval are analyzed, in order to study the geophysical mechanisms of thermospheric wind generation. Numerical simulations using a global, three-dimensional, time-dependent model of thermospheric dynamics were compared with the satellite data, and the results are discussed in detail. The wind distribution during the storm is shown in a series of color plates.

Rees, D.↗
NASA NTRS1985

A possible mechanism for the observed streaming of O(+) and H(+) ions at nearly equal speeds in the distant magnetotail

In recent years, O(+) and H(+) ions streaming away from the earth along geomagnetic field lines have been observed in the distant magnetotail region. In the present paper, it is suggested that the transverse acceleration of the ions occurs on auroral field lines at altitudes above the field-aligned potential drops, where ion beams and electrostatic hydrogen cyclotron (EHC) waves have been simultaneously observed. It is pointed out that the preferential acceleration of O(+) relative to H(+) occurs through the interaction of O(+) ions with weak EHC waves, as suggested by Singh et al. (1983). A quantitative explanation is provided for the observed relationship between the energies of O(+) and H(+) ions.

Singh, N.↗
NASA NTRS1985

Observations on the propagation, growth, and predictability of Gulf Stream meanders

During a three-year period, Gulf Stream positions determined by satellite infrared imagery on a grid northeast of Cape Hatteras have been correlated against 'inlet' path parameters (displacement from the mean position, angle, and curvature) monitored by an array of inverted echo sounders. By cross-spectral calculations between these measurements, the downstream coherences, phase speeds, and spatial growth rates were determined. The downstream path predictability from these inlet parameters was tested in a multiple input linear response model. The most energetic meanders, with periods of 33-50 days, remained highly coherent for 300 km downstream, roughly the dominant wavelength, with marginal coherence again at 500-575 km. Phase speeds are frequency dependent and decrease with distance downstream. For the 50- (33) day meanders, phase speeds decreased from 10 (17) km/d at the inlet to 6 (8) km/d at a distance downstream of about 550 km. The average growth rate (spatial e-folding wave number) over the entire region is 1.3 x 10 to the -3rd per km. Within 300 km of the inlet, the multiple coherence accounts for 55-65 percent of the total path-displacement variance, with displacement and angle being the best individual predictors in the first and last halves of this region, respectively.

Vazquez, J.↗
NASA NTRS1985

Upper-ocean velocity structure of Gulf Stream warm-core ring 82B

Acoustic-Doppler current profiling of warm-core ring (WCR) 82B revealed changes in the velocity structure over much of the ring's 7-month lifespan. As ring diameter decreased, peak speeds in the high-velocity region decreased from 0.8 m/s in April 1982 to 0.5 m/s in August 1982. Azimuthally averaged velocities revealed the core of WCR 82B to be in near solid-body rotation, with little measurable horizontal divergence at 100 m. In addition, potential vorticity was conserved in the ring core despite interactions with the Gulf Stream and large changes in ring size. Deviations from symmetry in WCR 82B were caused by superposition with the shelf-slope front, small cyclonic eddies, and upper-layer mean flow.

Joyce, T. M.↗
NASA NTRS1986

Experiments for the determination of convective diffusion heat/mass transfer to burner rig test targets comparable in size to jet stream diameter

The application of a recently formulated vapor transport theory to predict deposition rates of corrosive salts from alkali-seeded combustion gases of a small-capacity, high-velocity, atmospheric-pressure burner rig was hampered by the relatively large dimensions of the cylindrical deposit collector compared to the diameter of the combustion gas stream. The relative dimensions lead to a highly nonadiabatic combustion gas flow around the collector and necessitate two series of experiments. In the first series, mass transfer coefficients are determined by utilizing the naphthalene sublimation technique. The second series of experiments determines the dilution effect on the sodium species concentrations due to the entrainment of ambient air. This second series involves the measurement of the temperature variation along the surface of the collector under steady state conditions. Vapor deposition rates are determined exploiting this information and the results are found to compare favorably with experimentally obtained rates.

Santoro, G. J.↗
NASA NTRS1986

Intercontinental antenna arraying by symbol stream combining at ICE Giacobini-Zinner encounter

Deep space tracking stations on different continents were arrayed during the encounter of the International Cometary Explorer (ICE) spacecraft with the comet Giacobini-Zinner during September 9 through 12, 1985. This is the first time that telemetry signals received on different continents have been combined to enhance signal to noise ratio. The arraying was done in non-real time using the method of symbol stream combining. The improvement in signal to noise ratio was typically 2 dB over the stronger of the two stations in each array.

Hurd, W. J.↗
NASA NTRS1984

Free-jet feasibility study of a thermal acoustic shield concept for AST/VCE application-dual stream nozzles. Comprehensive data report. Volume 2: Laser velocimeter and suppressor. Base pressure data

Acoustic and diagnostic data that were obtained to determine the influence of selected geometric and aerodynamic flow variables of coannular nozzles with thermal acoustic shields are summarized in this comprehensive data report. A total of 136 static and simulated flight acoustic test points were conducted with 9 scale-model nozzles. Aerodynamic laser velocimeter measurements were made for four selected plumes. In addition, static pressure data in the chute base region of the suppressor configurations were obtained to assess the influence of the shield stream on the suppressor base drag.

Janardan, B. A.↗
NASA NTRS1986

Jet model for slot film cooling with effect of free-stream and coolant turbulence

An analysis was performed utilizing the model of a wall jet for obtaining equations that will predict slot film-cooling efficiency under conditions of variable turbulence intensity, flow, and temperature. The analysis, in addition to assessing the effects of the above variables, makes a distinction between an initial region and a fully developed region. Such a distinction is important in determining the role that the turbulence intensity of the coolant plays in effecting film-cooling effectiveness in the area of the slot exit. The results of the analysis were used in the correlation of the results of a well-designed film-cooling experiment. The result of the analysis and experiment was equations that predicted film-cooling efficiency within + or - 4% average deviation for lateral free-stream turbulence intensities up to 24% and blowing rates up to 1.9. These equations should be useful in determining the optimum quantity of cooling air requried for protecting the wall of a combustor.

Simon, Frederick F.↗
NASA NTRS1987

Secondary stream and excitation effects on two-dimensional nozzle plume characteristics

In order to design two-dimensional nozzle/ejector systems for future high performance aircraft, the basic engine exhaust plume velocity and temperature decay as effected by the secondary stream (ejector) and decay augmentation means must be assessed. Included in the assessment of the plume decay characteristics are the effects of nozzle aspect ratio and nozzle/ejector flow conditions. Nozzle/ejector plume decay can be enhanced by suitable excitation of the plume shear layers. Correlation of these factors are developed in a manner similar to those previously developed for conic and dual-flow nozzle plumes.

Vonglahn, Uwe H.↗
NASA NTRS1986

Structure and dynamics of corotating and transient streams in three dimensions

Current information on sources of interplanetary flows and their dynamical evolution are reviewed, and perturbations about the values given by Parker's model (1963) are considered. The radial evolution of a single corotating stream between the sun and 1 AU is described. Beyond 2 AU in the ecliptic, it is expected that forward shocks will be seen at high latitudes, with reverse shocks seen less probably.

Burlaga, L. F.↗
NASA NTRS1987

CSCM methodology for slot injection cooled cavity flow design in a high enthalpic stream

The CSCM method for the compressible Navier-Stokes equations is applied to study design factors in a slot injection cooled cavity flow in the side of a 2-D wedge body in a high enthalpy free stream. The flow geometry is being designed and will be tested in an arc jet tunnel at NASA-Ames Research Center. Objectives of the design are to provide adequate thermal protection for and minimize aero-optical distortion in the path above a window located in the bottom of the cavity. Among design issues, are the geometry of and flow conditions in the expanding section of the supersonic slot injection nozzle. Here, for straight walled nozzles, two geometries are considered for the upper nozzle lip between the hot, high speed outer flow and the colder, denser cooling flow. The two lip geometries - thick, square and thin, wedge - as the result of associated widely differing base/wake flows also exhibit different and interesting viscous-inviscid flow structures near the ramp termination to the cavity. For the thin lip case, the consequences on flow quality of off design nozzle conditions relative to matching pressure with the outer flow are explored.

Bardina, Jorge↗
NASA NTRS1987

Solar wind stream structure at large heliocentric distances Pioneer observations

Time profiles and histograms of plasma data from Pioneers 10 and 11 are examined for the period between 1975 and 1983. During this time, Pioneer 10 traveled between a heliocentric distance of 8.7 and 30.4 AU. The velocity structure of the solar wind at these heliocentric distances is found to have one of two distinct forms: approximately 70 percent of the time the solar wind has a nearly flat velocity profile. Occasionally, this flat velocity profile is accompanied by quasi-periodic variations in density and in thermal speed consistent with the concept that the 'corotating interaction regions' which are produced by the interaction of high- and low-speed streams at intermediate heliocentric distances are replaced by 'pressure regions' in the outer heliosphere. The remaining 30 percent of the time the solar wind is marked by large (50-200 km/s) long-term (30-120 days) shifts in the average solar wind velocity.

Gazis, P. R.↗
NASA NTRS1987

Multiplatform sampling (ship, aircraft, and satellite) of a Gulf Stream warm core ring

The purpose of this paper is to demonstrate the ability to meet the need to measure distributions of physical and biological properties of the ocean over large areas synoptically and over long time periods by means of remote sensing utilizing contemporaneous buoy, ship, aircraft, and satellite (i.e., multiplatform) sampling strategies. A mapping of sea surface temperature and chlorophyll fields in a Gulf Stream warm core ring using the multiplatform approach is described. Sampling capabilities of each sensing system are discussed as background for the data collected by means of these three dissimilar methods. Commensurate space/time sample sets from each sensing system are compared, and their relative accuracies in space and time are determined. The three-dimensional composite maps derived from the data set provide a synoptic perspective unobtainable from single platforms alone.

Smith, Raymond C.↗
NASA NTRS1987

Secondary stream and excitation effects on two-dimensional nozzle plume characteristics

In order to design two-dimensional nozzle/ejector systems for future high performance aircraft, the basic engine exhaust plume velocity and temperature decay as effected by the secondary stream (ejector) and decay augmentation means must be assessed. Included in the assessment of the plume decay characteristics are the effects of nozzle aspect ratio and nozzle/ejector flow conditions. Nozzle/ejector plume decay can be enhanced by suitable excitation of the plume shear layers. Correlations of these factors are developed in a manner similar to those previously developed for conic and dual-flow nozzle plumes.

Von Glahn, Uwe H.↗
NASA NTRS1987

Some models of the Geminids meteor stream formation

Further development of methods of investigations of meteor shower structure and a great deal of observational data have made it possible to obtain a precise flux density profile along the Earth's orbit for the Geminids meteor shower. This curve proved to be adequately described by a exponential law. Examined are: (1) which ejection model will fit the observed shower structure; and (2) to what extent the subsequent process of evolution modifies the formed structure. The following conclusions are drawn: (1) When studying the mechanism of formation of meteor streams, it is necessary to take into consideration the velocity distribution of particles that have been ejected from the parent body; (2) On the basis of the observed density variations, it is possible to determine what kind of ejection takes place (a single ejection or that around an orbital arch); and (3) The original structure of the Geminids cross section persists for no more than 1,500 to 2,000 years.

Belkovich, O. I.↗
NASA NTRS1987

First-order Fermi acceleration in the two-stream limit

A study of the first-order Fermi mechanism for accelerating cosmic-rays at relativistic and nonrelativistic shocks is carried out by using the two-stream approximation. Exact steady-state analytic solutions illustrating the shock acceleration process in the test-particle limit in which monoenergetic (relativistic) seed particles enter the shock through an upstream free-escape boundary are obtained. The momentum spectrum of the shock accelerated particles consists of a series of Dirac delta distributions corresponding to particles that have undergone an integral number of acceleration cycles. Since particles in the model have a finite fixed escape probability from the shock and the particle momenta p are equally spaced in log p, the envelope of the delta functions series is a power law in momentum. The solutions are used to discuss time-dependent aspects of the shock acceleration process in terms of the finite cycle time, escape probability, and momentum change per cycle that can be deduced from the steady-state model. The length-scale over which the accelerated particles extend upstream of the shock is shown to depend upon the particle energy, with the higher energy particles extending further upstream. This effect is shown to be intimately related to the kinematic threshold requirement that the particle speed exceed the fluid speed in order for particles to swim upstream of the shock and participate in the shock acceleration process.

Bogdan, T. J.↗
NASA NTRS1987

Jet stream velocity errors in general circulation models

The longitude and time dependence of excessive wind speed errors above subtropical jets in current GCM forecasts is studied for 14 five-day winter forecasts using the NASA Goddard Laboratory for Atmospheres fourth-order GCM. Several distinct phenomena, which may be divided into four categories, are found to contribute to the excess winds. These categories are: (1) error growth above the jet near the Himalayas; (2) error growth above the jet initiated elsewhere followed by advection; (3) tropical moisture bursts appearing in equatorial regions and migrating northeastward to merge with and distort the jet; and (4) undulatory growth of waves in the meridional component of the jet stream velocity. The results of additional sensitivity studies of the Himalayan region error are also reported.

Tenenbaum, J.↗